Spectroscopy of electronic states of metals with a scanning tunneling microscope
by W. J. Kaiser, R. C. Jaklevic
We have constructed a scanning tunneling microscope (STM) and have obtained current-voltage derivative spectra from metal surfaces. For Au(111) we have observed an electronic surface state 0.4 eV below the Fermi energy. This state has previously been observed with photoemission and oxide tunneling experiments. We have also observed strong peaks in spectra obtained from Pd(111) which we identify with surface states and effects derived from bulk energy bands. In the voltage range investigated here, tunneling takes place through the entire vacuum gap between the metallic tip of the microscope and the surface of the sample being examined. The STM spectroscopy results reported here are compared with previous experimental work and theory. These intrinsic surface states are the first which have been observed with the STM and demonstrate its unique applicability to the investigation of surface electronic structure.